1. Field of the Invention
This invention relates to filling tools (so-called caulking guns) used mainly for repairing operations of building materials or the like for the purpose of waterproofing, such as repairing operations of cracks or gaps in the outer wall of a residential building and repairing operations of a joint between a bathtub and a wall surface of a bathroom, by filling materials, such as a silicon type filling material, (hereinafter simply referred to as caulking materials).
2. Description of the Related Art
For example, a caulking material known as a silicon sealant is commercially available on the market in a form of a cartridge filled with a fixed amount of the material. The cartridge may be set in a dedicated caulking gun to be used for the filling operation.
In general, the caulking gun includes a lever in the form of a trigger that can be pulled by the user grasping a handle portion of the caulking gun to move an push rod, whereby the caulking material can be extruded from a nozzle of the cartridge. In the case of this completely manual type caulking gun, great fatigue is involved as a result of the repetition of the extruding operation. In view of this, there has been provided an electric caulking gun using an electric motor as a drive source. Techniques related to this electric caulking gun are disclosed, for example, in JP-A-8-257465 (also published as Japanese Patent No. 3598565), JP-A-58-137465, and U.S. Pat. No. 4,615,469 (Also published as JP-A-59-222251). In the electric caulking guns as disclosed in these publications, the electric motor is started to move the push rod when a switch lever is operated to be turned on. Therefore, unlike the manual type caulking gun, in which the operation force of the lever generates the extrusion force, the user can easily perform the filling operation repeatedly.
However, in general, the cartridge is set to extend forward from the front central portion of a main body of the caulking gun. In this connection, the push rod is necessary to be set to extend in the advancing and retracting direction across the central portion with respect to the widthwise direction of the main body.
Due to this arrangement of the push rod, the electric motor is necessary to be position to project laterally from the main body by a relatively large distance, leading to unfavorable unbalance in weight of the caulking gun in the right and left direction.
Therefore, there has been a need in the art for a technique of improving the balance in weight of a may body of an electric caulking gun.